Studies in the Gait Laboratory of the Department of Rehabilitation Medicine have focussed on the control of balance. Simultaneous measurement of body angles, foot-floor forces and multiple EMGs are possible. Studies in normal subjects have revealed insights into the biomechanical effects of postural muscle activity. Similar studies have been initiated in patients with cerebellar disturbance and Parkinson's Disease. Two patients with orthostatic tremor have also been investigated. In patients with Parkinson's Disease there was a positive correlation between circulating levels of dopamine and cognitive motor capabilities in a choice reaction time situation but not in a simple reaction time situation. In normal subjects, triggered muscle responses produced by stopping voluntary movements were similar to muscle responses generated when subjects initiated a voluntary movement from the stopped location, thereby suggesting that triggered and voluntary reactions are mediated by similar central nervous system mechanisms. The study of motor control in hemiplegia is being planned and apparatus is being prepared. Patients with discrete brain lesions will be studied; patients with strokes will be the main group, and many patients will be followed serially from onset of the disorder to recovery. Preliminary studies with positron emission tomography (PET) of normal subjects have shown that it is difficult to identify cortical areas active with voluntary movement using fluoro-deoxy-glucose (FDG) as the tracer. Further studies are planned with oxygen-15-water which will probe blood flow rather than glucose metabolism.